The invention relates to a method for saving electric power in apparatus having the function of optical communication using optical signals, a method for using such apparatus, and an optical communication system structured thereby.
In an optical communication apparatus, while the apparatus is inactive i.e. in the standby state (or standby time), the power saving is attempted from the standpoint of eliminating or reducing the energy. An example of the optical communication apparatus taking such measures for the power saving has already been made open to the public by a KOKAI (unexamined patent publication) No. 6-152518. This publication teaches a power saving technology which is adaptable to the network terminal (NT) installed in a user's house subscribing to the optical line transmission system. More concretely, the publication describes, in the 2nd column, lines 20 to 23, that the power supply to a light emitting element circuit in the network terminal (NT) is cut off while the terminal is in the standby state. The publication further describes, in the 3rd column, lines 22 to 27, that the power supply to a circuit for a light receiving element and an amplifier used therefor is cut off for a specific period of time during the standby time.
In case of the above-mentioned conventional technology, however, a cut-off period of the power supply to the circuit for the light receiving element and the amplifier therefor in the standby time is made roughly a half of the standby time (see the 3rd column, lines 42 to 43 of the publication).
Consequently, according to the above conventional technology, the power supply to the circuit of the light receiving element and the amplifier therefor is still allowed for about a half of the standby time.
Now, let us discuss this respect further a little in detail. In case of the above conventional technology, as will be apparent from the description in the 3rd column, lines 37 to 43 and FIG. 2 of the above publication, the network terminal (NT) repeats the ON/OFF operation of the power source for the circuit of the light receiving element and the amplifier therefor at a twice frequency of the optical burst signal which is inputted from an office line terminal (LT).
According to this way, as the power supply to the circuit of the light receiving element and the amplifier circuit therefor is carried out intermittently, the power saving in the circuit of the light receiving element and the amplifier circuit therefor may be attained although detection of the burst signal (here, regarded as a kind of an optical signal calling for communication start) can not help being carried out intermittently.
In case of this conventional technology, however, as the power is still supplied to the circuit of the light receiving element and the amplifier therefor for about a half of the standby time, the power saving effect during the standby time has not always produced a satisfactory result.
Accordingly, it is desired to establish a more effective method for the power saving in the circuit system for use in the light receiving element and an optical communication apparatus capable of preferably executing the method.